1. Field of the Invention
The present invention relates to a running control apparatus and an alarm apparatus for vehicles, and in particular to a running control apparatus for vehicles which performs running control to allow the subject vehicle to follow a preceding vehicle and makes running control so that the subject vehicle does not collide with an obstacle, and an alarm apparatus for vehicles for preventing collision with a preceding vehicle or an obstacle by generating an alarm.
2. Related Art
Conventionally, as a following running control apparatus for controlling following running of an automobile, an apparatus is known in which distance and relative speed between a preceding vehicle and a subject vehicle are used to control vehicle velocity so that the distance between the preceding vehicle and the subject vehicle is kept at a safe distance. (Japanese Patent Laid-open No. 61-77533). In addition, an apparatus for controlling distance between vehicles is known in which an acceleration of a preceding vehicle is used to change the distance between that vehicle and the subject vehicle (Japanese Utility Model Laid-open No. 2-133800). Further, an apparatus is known in which distance between a preceding vehicle and a subject vehicle is used to determine target vehicle speed. This target vehicle speed is corrected on the basis of relative acceleration, thereby controlling vehicle speed (Japanese Utility Model Laid-open No. 3-295000).
However, in the conventional apparatus in which vehicle speed is controlled according to vehicle distance and relative velocity, problems arise in that a period of time is required, with respect to the deceleration of the preceding vehicle, for the distance between the vehicles and relative speed to change by predetermined values, and the response characteristic to the rapid deceleration of the preceding vehicle deteriorates. Thus, the driver of the subject vehicle sometimes feels that the timing of deceleration is late.
In addition, the apparatus for controlling the distance between vehicles in which the acceleration of the preceding vehicle is used to change the target distance between the vehicles has problems in that when the target distance between vehicles is shortened in accordance with a positive acceleration of the preceding vehicle (the nearing direction is positive), a time lag occurs until the preceding vehicle reaches the target distance between the vehicles, the response characteristic to the rapid deceleration of the preceding vehicle deteriorates in the same manner as described above, and it is felt that the timing of the deceleration of the subject vehicle is late. On the other hand, when the target distance between vehicles is lengthened in accordance with the deceleration of the preceding vehicle, the response characteristic to rapid deceleration of the preceding vehicle is improved. However, there is unnecessary excessive deceleration.
Further, in the case of the apparatus for controlling vehicle speed in which the target vehicle velocity is corrected on the basis of relative acceleration, it is difficult to calculate a correction amount which is adequate for a driver, and also difficult to adequately control the starting time for decelerating of the subject vehicle.
In addition, as a running control apparatus which controls a subject vehicle so as to follow a preceding vehicle, Japanese Patent Laid-open No. 61-77534 discloses a technique in which it is judged whether or not the deceleration of the subject vehicle is necessary based on distance and relative speed between the preceding vehicle and the subject vehicle. If it is judged that deceleration is necessary, then in accordance with the magnitude of the difference between the deceleration of the subject vehicle and a predetermined deceleration reference value, an appropriate operation is selected from one of the deceleration operations--letting off the throttle, an exhaust brake operation, a down shifting operation, and a brake operation so as to decelerate. In such a manner, the judgment of deceleration has been made in the prior art on the basis of the distance between vehicles and the relative speed of the preceding vehicle.
However, for example, even if the preceding vehicle decelerates rapidly, there is a short time lag until changes in relative speed and distance between the vehicles are detected. Accordingly, the above-mentioned apparatus in which deceleration is controlled on the basis of the distance between vehicles and relative speed has had problems in that a period of time is required from the time that the preceding vehicle begins rapid deceleration until the execution of a strong deceleration (for example, a sudden braking operation) which corresponds to the rapid deceleration of the preceding vehicle, and a sense of incongruity on the part of the driver. In addition, in order to resolve the above-mentioned problems, for example, if a large value is set as the deceleration reference value, the decelerating operation is selected to allow the deceleration of the subject vehicle to coincide with the reference value. As a result, deceleration is performed at an unnecessarily and excessive level with respect to the gradual deceleration of the preceding vehicle. Accordingly, a sense of incongruity is given to the driver.
In order to prevent accidents such as rear-end collisions with preceding vehicles and the like, various apparatuses for generating an alarm to a driver has been proposed. Japanese Patent Laid-open No. 59-105587 discloses a vehicle collision alarm apparatus in which a distance between a preceding vehicle and a subject vehicle is detected, an alarm is sounded when the distance between the vehicles becomes smaller than a reference value. At the same time the above-mentioned reference value is changed in accordance with the relative speed of the preceding vehicle. In addition Japanese Patent Laid-open No. 4-304600 discloses a running state judging apparatus in which a future distance between vehicles is predicted on the basis of a vehicle distance, speed of the subject vehicle and speed of a preceding vehicle in order to determine whether or not a dangerous state has developed.
However, for example, in a case in which the preceding vehicle rapidly decelerates and the like, there is a short time lag until the distance change between the vehicles are detectable by not less than a predetermined value. Therefore, the above-mentioned apparatus in which the alarm is sounded on the basis of the distance between vehicles has had problems in that it is difficult to sound the alarm within a short time period after the preceding vehicle starts rapid deceleration. In addition, there has been a problem that, for example, when the reference value as a threshold value to generate the alarm is made large in order to resolve the above-mentioned problem, the alarm is sometimes generated even when the driver determines the circumstances to be safe, thereby giving the driver a sense of incongruity.
In any one of the above-mentioned apparatuses, danger is judged on the basis of the magnitude of the distance between vehicles with respect to the preceding vehicle, and an alarm is sounded, for example, in a case in which a driver does not notice that the distance between vehicles has become short due to the deceleration and the like of the preceding vehicle. Owing to this alarm, the driver can recognize states in which the distance between the vehicles becomes short, which makes the risk of having a rear-end collision with the preceding vehicle. The driver can then decelerate the vehicle by operating a brake and the like, so as to prevent the occurrence of a rear-end collision with the preceding vehicle.